Ferrite magnetic material and method for producing hexagonal w type ferrite magnetic material

Abstract

The present invention provides a ferrite magnetic material comprising as a main constituent a compound represented by a composition formula, AFe 2+ a Fe 3+ b O 27 (wherein 1.1≦a≦2.4, 12.3≦b≦16.1; and A comprises at least one element selected from Sr, Ba and Pb), and also comprising as additives a Ca constituent in terms of CaCO 3 and a Si constituent in terms of SiO 2 so as to satisfy the relation CaCO 3 /SiO 2 =0.5 to 1.38 (molar ratio). By making the relation CaCO 3 /SiO 2 =0.5 to 1.38 (molar ratio) be satisfied, the coercive force (HcJ) and the residual magnetic flux density (Br) can be made to simultaneously attain high levels.

1 . A ferrite magnetic material characterized by comprising as a main constituent a compound represented by a composition formula, AFe2+aFe3+bO27 (wherein 1.1≦a≦2.4, 12.3≦b≦16.1; and A comprises at least one element selected from Sr, Ba and Pb), and as additives a Ca constituent in terms of CaCO3 and a Si constituent in terms of SiO2 so as to satisfy the relation CaCO3/SiO2=0.5 to 1.38 (molar ratio).  
   
   
       2 . The ferrite magnetic material according to  claim 1 , characterized in that said a satisfies the relation, 1.5≦a≦2.4.  
   
   
       3 . The ferrite magnetic material according to  claim 1 , characterized in that said b satisfies the relation, 12.9≦b≦15.6.  
   
   
       4 . The ferrite magnetic material according to  claim 1 , characterized in that CaCO3/SiO 2=0.6  to 1.1 (molar ratio).  
   
   
       5 . The ferrite magnetic material according to  claim 1 , characterized in that said ferrite magnetic material constitutes any of a ferrite sintered magnet, a ferrite magnet powder, a bonded magnet in which said ferrite magnetic material is dispersed as a ferrite magnet powder in a resin, and a magnetic recording medium in which said ferrite magnetic material is contained as a film-like magnetic phase.  
   
   
       6 . The ferrite magnetic material according to  claim 5 , characterized in that said ferrite sintered magnet is 0.8 μm or less in mean grain size.  
   
   
       7 . The ferrite magnetic material according to  claim 1 , characterized in that said ferrite magnetic material comprises a hexagonal W-type ferrite as a main phase.  
   
   
       8 . A method for producing a hexagonal W-type ferrite magnetic material characterized by comprising the steps of: 
 (a) obtaining a raw material powder comprising A (wherein A comprises at least one element selected from Sr, Ba and Pb) and Fe;    (b) obtaining a calcined body by maintaining said raw material powder at a predetermined temperature for a predetermined time; and    (c) milling said calcined body,    wherein CaCO3 and/or SiO2 are added before and/or after said step (b) so that the hexagonal W-type ferrite magnetic material comprises a Ca constituent in terms of CaCO3 and a Si constituent in terms of SiO2 so as to satisfy the relation of molar ratio CaCO3/SiO2=0.5 to 1.38.    
   
   
       9 . The method for producing a hexagonal W-type ferrite magnetic material according to  claim 8 , characterized by further comprising a step (d) for sintering the milled powder obtained in said step (c).  
   
   
       10 . The method for producing a hexagonal W-type ferrite magnetic material according to  claim 8 , characterized by preparing a ferrite magnet powder by pulverizing the sintered body obtained in said step (d).  
   
   
       11 . The method for producing a hexagonal W-type ferrite magnetic material according to  claim 8 , characterized by preparing a ferrite magnet powder by said step (c).  
   
   
       12 . The method for producing a hexagonal W-type ferrite magnetic material according to  claim 8 , characterized by adding a fraction of said A after calcining.  
   
   
       13 . The method for producing a hexagonal W-type ferrite magnetic material according to  claim 8 , characterized in that said Ca constituent is added in said step (a) in an amount of 0.01 wt % or more and less than 1.0 wt % in terms of CaCO3 in relation to said raw material powder.  
   
   
       14 . The method for producing a hexagonal W-type ferrite magnetic material according to  claim 9 , characterized in that: 
 said Ca constituent is added in said step (a) in an amount of 0.01 wt % or more and less than 1.0 wt % in terms of CaCO3 in relation to said raw material powder; and    said Ca constituent is further added in an amount of 0.1 to 2.0 wt % in terms of CaCO3 after said step (b) and before said sintering step (d).